Venting of molds

A mold comprising a molding cavity defined by molding walls made of one or more materials, each molding wall having an air-tight molding surface defining a portion of the shape of the outer surface of the object to be molded, a mold venting means venting the mold cavity and a supplementary venting means venting the mold cavity at a lesser rate of flow than the mold venting means at the molding temperature and pressure, said supplementary venting means including at least one hole extending from said molding surface through a molding wall so as to place the molding cavity in communication with the outside of said mold, and a plug filling and closing the hole on insertion of the plug in the hole and having an air-tight end face flush with said molding surface so as to constitute a portion of the molding surface, said plug on insertion occupying precisely the entire surface of said hole in said molding surface, the plug being made of a material the hardness of which is substantially less than the hardness of the material surrounding the hole, the plug having, before mounting in the hole, a cross section circumscribed in the cross section of the hole on at least the face intended to be flush with the molding surface, the plug being force-fitted in the hole.